Storage area networks, also referred to as SANs, are dedicated networks that connect one or more systems, referred to as hosts or storage clients, to storage devices and storage subsystems. Data storage on a SAN may be accomplished using a number of individual storage devices or subsystems that each store one or more volumes of data. Furthermore, data storage may also be accomplished using what is known as logical volumes in a distributed network data storage system, in which there are two or more network data storage devices utilized and a mechanism exists for defining the logical volume that physically extends over the two or more network data storage devices. In such a distributed storage system, the hosts perform storage operations on the logical volume that, from the perspective of the hosts, appears to be a single storage device. For example, a network computer system employing distributed network storage may be comprised of: (a) two network storage servers; (b) a computer; and (c) a network for facilitating data transfers between the servers and the computer. The computer comprises a driver (a program that allows an operating system to communicate with a device) for each of the network storage devices and a logical volume manager that controls the drivers so as to define a logical or virtual volume that extends over the two network storage servers.
Such SANs are commonly used for data storage where the data is required to be highly available. Such high availability is necessary because often the customers storing the data on the SAN need immediate access to the data, and any unavailability may result in lost time, lost revenue, and/or dissatisfied customers. In order to provide high availability, such SANs commonly employ multiple failure recovery and backup systems, including storing data in a redundant fashion and providing backup storage devices, among others. Another key characteristic of such data storage systems is the time required to complete storage operations. In order to provide relatively fast storage operations, such systems commonly employ high bandwidth network connections and a high bandwidth network. For example, fibre channel is presently one of the leading technologies for SANs. Furthermore, host computers may issue storage I/O commands to multiple storage devices in parallel in order to provide increased performance, with each storage device returning a portion of required data that may then be assembled by the host computer.